Aquatic Sciences Meeting, Albuquerque 2001

SS40 Long-Term Research Programs in the Twenty-first Century (Spatial and Temporal Connections)

Date: Thursday, February 15, 2001, Time: 2:15:00 PM

Location: Ruidoso/Pecos

Cozzarelli, I, M, US Geological Survey, Reston, USA, icozzare@usgs.gov

Bekins, B, A, US Geological Survey, Menlo Park, USA, babekins@usgs.gov

Baedecker, M, J, US Geological Survey, Reston, USA, mjbaedec@usgs.gov

Eganhouse, R, P, US Geological Survey, Reston, USA, eganhous@usgs.gov

LONG-TERM ASSESSMENT OF NATURAL ATTENUATION PROCESSES AT AN AQUIFER CONTAMINATED WITH CRUDE OIL

The prevalence of hydrocarbon-contaminated aquifers and the realization that technological and monetary constraints limit engineered remediation, have resulted in an increased reliance on natural processes to control migration of contaminant plumes. The assessment of natural attenuation as a remedial option requires an understanding of the long-term fate of the contaminant and contaminant controls. At the USGS Toxic Substances Hydrology research site near Bemidji, MN, the long-term study of the crude-oil contaminated aquifer has shown that the shape and extent of the contaminant plume changed as redox reactions progressed over time. Early indications of plume shrinkage were associated with degradation of hydrocarbons coupled to iron reduction. The subsequent depletion of the Fe(III) oxides caused the zone of maximum concentrations of BTEX to move downgradient as the reactions shifted to methanogenesis. Analysis of sediment and water, collected at closely spaced vertical intervals, provide insight into the evolution of redox zones and migration of hydrocarbons at the centimeter scale. Some contaminants, such as ortho-xylene, that appeared not to be moving downgradient from the oil on the basis of plume-scale observation well data, are migrating in thin layers as the aquifer evolves to methanogenic conditions in these zones. In this system, the long-term sustainability of the electron acceptors is key to predicting the ultimate fate of the hydrocarbons.

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Aquatic Sciences Meeting, Albuquerque 2001

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